Shielded cable

ABSTRACT

An electric power cable with a semiconducting jacket has drain conductors in the form of thin metallic strips embedded in the jacket and firmly bonded to it by means of an adhesive coating.

United States Patent Arnaudm, Jr. et al. [45] Ma 30, 1972 54] SHIELDED CABLE 3,564,111 2/1971 Breitenbach ..174/115 x 3,474,189 10/1969 Plate et a1 ..174/1l5 [721 lnvemrs= 1 1 Arf'audin, Eden, NC; 3,424,631 1/1969 Peacock ..174/120 R Manon, 3,351,706 11/1967 Gnerre et a1. ....174/105 so [73] Assign; Anaconda wire and Cable Company 3,297,814 1/1967 McClean et a1.... ..174/1 15 X 1 3,115,542 12/1963 Palandn et a]. ..174/102X [22] Filed: May 10, 1971 1 pp No: 41 9 5 Primary ExaminerE. A. GOldbElg Assistant Examiner-A. T. Grimley Alt0rneyVictor F. Volk [52] US. Cl. ..174/l15, 174/36, 174/102 SC,

174/105 SC, 174/113 R, 174/120 SC [57] ABSTRACT [51] lnt.C1. ..H0lb 9/02 [58] Field f "17402 R 102 SC, 105 SC An elecmc power cable w1th a sem1conduct111g acket has 174/106 SC, 1 13 R 1 15 117 R, l 17 A, 1 17 FF, drain conductors in the form of th1n metalhc stnps embedded 107 120 SC, 127, 120 R 36 in the jacket and firmly bonded to it by means of an adhesive coating.

[56] References Cited UNITED STATES PATENTS 8 Claims, 3 Drawing Figures Patented May 30, 1972 I N VliN ()RS E. H. ARNAUDIN Jr. w. E MORRISON y /M SHIELDED CABLE BACKGROUND OF THE INVENTION This invention comprises an improvement in the art of electric cables comprising semiconducting jackets and embedded drain conductors. Such cables have particular application for direct burial and have been described in Plate et al. U.S. Pat. Nos. 3,474,189 and 3,517,613 wherein the drain conductors are comprised of undulatory wires. The undulatory shaping of the drain wires in these cables has been necessitated by the need for cable flexibility.

SUMMARY We have found that foil strips of great width-to-thickness ratio can be substituted for undulatory wires without damage due 'to cable flexing by bonding these strips to the insulation or jacket material. For this and other useful purposes we have invented an electric power cable comprising a metallic conductor, a wall of electrical insulation surrounding the conductor, a wall of semiconducting jacketing material surrounding the wall of insulation and a plurality of metal strips laid longitudinally in spaced positions around the perimeter of the cable externally of the wall of insulation and internally of the outer surface of the wall of semiconducting material. The strips comprise a thin coating of adhesive, preferably electrically conducting, which bonds it to at least one of the walls. These strips may be entirely embedded in the semiconducting material which may advantageously comprise longitudinal bosses within which the strips may be contained. The semiconducting material may advantageously comprise a polyolefin which may be chlorinated and the adhesive may comprise the copolymer of ethylene and acrylic acid. The strips will be comprised of copper or aluminum.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a pictorial view of one embodiment of our invention.

FIG. 2 shows a pictorial view of another embodiment of our invention.

FIG. 3 shows a sectional view of still another embodiment of our invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In the figures a metallic power conductor 1 l which may be considered as conventional and as solid or comprised of a plurality of strands is surrounded by a strand shielding layer 12, also conventional, of semiconducting compound. A heavy wall of insulating material 13 surrounds the conductor and strand shielding in the usual manner. Referring first to FIG. 2 the wall 13 has extruded over it a semiconducting jacket 14 within which there are embedded strips 16 of drain conductor foils. As shown, the foils are embedded about half the depth of the jacket, the greater depth providing greater mechanical resistance against ejection from the cable during a high current fault. As shown, each of the foil strips 16 is coated with a layer of adhesive 17 which bonds firmly to the material of the jacket wall 14. The adhesive 17 is preferably rendered electrically conducting in a known manner as by the inclusion of graphite or metallic particles so that the jacket 14 and drain conductors reinforce each other electrically. The great surface area of the strips 16 provides a large bonding area for the adhesive and provides a very substantial advantage with regard to resistance against the disruptive mechanical forces which tends to tear them radially apart under severe electrical stresses. The drain foils 16 will not be greater than 20 mils thick to get the benefit of our invention and will have a width at least five times the thickness. Preferably the strips will have a thickness between 3 and 8 mils and a width of to 100 times the thickness. The adhesive bonding to the jacket wall has an important function of preventing the strips from crinkling and eventually failing from repeated flexure of the cable.

A suitable adhesive for bonding the strips to olefinic material has been disclosed in U.S. Pat. No. 3,315,025 to comprise an ethylene-acrylic copolymer. Such adhesives are commercially available and can be rendered electrically conducting by the introduction into the composition of graphite, conducting black, or metallic particles in a known manner. The coating 17 will have a thickness from 0.5 to about 2 mils. It is applied to the strips 16 prior to the introduction of the strips into the cable structure, by'any of various known methods such as extrusion, spray coating, solution coating, and hot rolling, of a film of the adhesive to the metal. The adhesive is not wet or tacky on the strips but is softened by the heat of extrusion of the jacket to form a firm bond on the strips being introduced into the extrusion die during the jacket extrusion operation. The jacket 14 may be comprised of any of a plurality of suitable cable jacket materials such as polyethylene or other polyolefin, neoprene, chlorosulfonated polyethylene, and polyvinyl chloride that have been compounded to be semiconducting by the inclusion of graphite or acetylene carbon black or other electrically conducting additives.

In the embodiment shown in FIG. 1, longitudinal bosses 18 have been extruded onto the jacket and the strips 16 are included in these bosses. This has been accomplished by guiding the strips into the appropriate position in the extrusion die during the extrusion operation and has the advantage of economizing on jacketing compound. In FIG. 3 strips 19 of metal foil are applied directly to the outer surface of the insulation layer 13 and bonded firmly to this layer by a coating 21 of adhesive, which is not necessarily electrically conducting, provided that it is entirely free from voids or pinholes. Here it is important that the surface of the insulation should be in close, void-free, contact with the shielding layer. In the embodiments of FIGS. 1 and 2 this has been achieved by extruding the semiconducting jacket directly over the insulation. In the embodiment of FIG. 3, if the coating 21 is conducting it will comprise a portion of the shielding and if it is not conducting it will comprise a portion of the insulation. In either case no voids will be present at the insulation-shielding interface. Where thin foils are used for the strips 19, a coating on the insulation side only, will be sufficient to keep them from buckling, but where the gage approaches 20 mils it is highly desirable to apply adhesive to the outer jacket side surface of the strips 19, as well. In all embodiments it is advantageous, especially for thicker strips, to have adhesive coatings on the edges, as well as the broad surfaces.

We have invented'new and useful power cables of which the foregoing description has been exemplary rather than definitive and for which we desire an award of Letters Patent as defined in the following claims.

We claim:

1. An electric power cable comprising:

A. a metallic conductor,

B. a wall of electrical insulation surrounding said conductor,

C. a wall of semiconducting jacketing material surrounding said wall of insulation,

D. a plurality of metal strips laid longitudinally in spaced positions around the perimeter of said cable externally of said wall of insulation and internally of the outer surface of said wall of semiconducting material,

E. a thin coating of adhesive on said strips, said adhesive bonding said strips to at least one of said walls.

2. The cable of claim 1 wherein said wall of semiconducting material directly surrounds the entire surface of said wall of insulation and said strips are embedded in said semiconducting material.

3. The cable of claim 1 comprising a plurality of longitudinal bosses in said wall of semiconducting material, said strips being contained in said bosses.

4. The cable of claim 1 wherein said strips comprise aluminum.

5. The cable of claim I wherein said strips comprise copper.

6. The cable of claim 1 wherein said adhesive is electrically conducting.

7. The cable of claim 1 wherein said semiconducting material comprises a polyolefin.

8. The cable of claim 7 wherein said adhesive comprises the copolymer of ethylene and acrylic acid.

* l k k 

2. The cable of claim 1 wherein said wall of semiconducting material directly surrounds the entire surface of said wall of insulation and said strips are embedded in said semiconducting material.
 3. The cable of claim 1 comprising a plurality of longitudinal bosses in said wall of semiconducting material, said strips being contained in said bosses.
 4. The cable of claim 1 wherein said strips comprise aluminum.
 5. The cable of claim 1 wherein said strips comprise copper.
 6. The cable of claim 1 wherein said adhesive is electrically conducting.
 7. The cable of claim 1 wherein said semiconducting material comprises a polyolefin.
 8. The cable of claim 7 wherein said adhesive comprises the copolymer of ethylene and acrylic acid. 